Bootstrap Multiselect Skeleton

HTML

<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/css/bootstrap.css">
<link rel="stylesheet" href="http://davidstutz.github.io/bootstrap-multiselect/dist/css/bootstrap-multiselect.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/js/bootstrap.js"></script>
<script src="http://davidstutz.github.io/bootstrap-multiselect/dist/js/bootstrap-multiselect.js"></script>
<script src="https://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.min.js"></script>
<div class="container">
    <div class="row">
        <div class="col-sm-8 col-sm-offset-2">
            <div class="page-header">
                <div class="alert alert-info" role="alert">
                    <h4>This demo shows how to integrate JQuery-validation and the Bootstrap framework.</h4>
                    <ul>
                        <li><a href="http://getbootstrap.com/" class="alert-link">Bootstrap home project</a>.</li>
                    </ul>
                </div>
            </div>

            <div class="panel panel-default">
                <div class="panel-heading">
                    <h3 class="panel-title">Simple Form</h3>
                </div>
                <div class="panel-body">
                    <form id="signupForm" method="post" class="form-horizontal" action="">
                        <div class="form-group">
                            <label class="col-sm-4 control-label" for="firstname">First name</label>
                            <div class="col-sm-5">
                                <input type="text" class="form-control" id="firstname" name="firstname" placeholder="First name" />
                            </div>
                        </div>

                        <div class="form-group">
                            <label class="col-sm-4 control-label" for="lastname">Last name</label>
                         ...

CSS

/*the below fixes the issue where bootstrap multiselect plugin show radio button for single select dropdown*/

.multiselect-container input[type=radio] {
    display: none;
}

JavaScript

$("#signupForm").validate({
    ignore: [],
    rules: {
        firstname: "required",
        lastname: "required",
        food: "required",
        username: {
            required: true,
            minlength: 2
        },
        password: {
            required: true,
            minlength: 5
        },
        confirm_password: {
            required: true,
            minlength: 5,
            equalTo: "#password"
        },
        email: {
            required: true,
            email: true
        },
        agree: "required"
    },
    messages: {
        firstname: "Please enter your firstname",
        lastname: "Please enter your lastname",
        food: "Fruit is required to enter",
        username: {
            required: "Please enter a username",
            minlength: "Your username must consist of at least 2 characters"
        },
        password: {
            required: "Please provide a password",
            minlength: "Your password must be at least 5 characters long"
        },
        confirm_password: {
            required: "Please provide a password",
            minlength: "Your password must be at least 5 characters long",
            equalTo: "Please enter the same password as above"
        },
        email: "Please enter a valid email address",
        agree: "Please accept our policy"
    },
    errorElement: "em",
    errorPlacement: function(error, element) {
        // Add the `help-block` class to the error element
        error.addClass("help-block");

        if (element.prop("type") === "checkbox") {
            error.insertAfter(element.parent("label"));
        } else if (element.hasClass('multiselect')) {
            error.insertAfter(element.next('.btn-group'))
        } else {
			error.insertAfter(element);
		}
    },
    highlight: function(element, errorClass, validClass) {
        $(element).parents(".col-sm-5").addClass("has-error").removeClass("has-success");
    },
    unhighlight: function(element,...